Kidney function changes after single-dose administration of borocaptate sodium (mercaptoundecahydro-closo- dodecaborate, B12H11SH, BSH) were studied in rats. Changes of glomerular filtration rate (GFR) measured as 14C-inulin clearance, renal plasma flow rate (3H-p-aminohippuric acid clearance) and urine flow rate (UFR) after a slow intravenous injection of BSH (25 mg/kg b.w.) were investigated in rats under pentobarbital anaesthesia. It was found that a slow BSH injection induces a gradual decrease of renal plasma flow and glomerular filtration rate resulting in an almost constant reduction of the filtration fraction. These alterations were accompanied by a temporary increase of urine flow rate. Although a direct effect of BSH on the nephron cannot be excluded, it is suggested that the observed changes in kidney function might at least partly be mediated by disturbances in the function of the cardiovascular system following BSH injection. The role of the dianionic sulfhydryl group present in the borocaptate molecule in inducing these renal functional changes is discussed.
The differences in glomerular filtration rate (GFR) based on creatinine clearance (Cer) or obtained by the more exact methods are caused mainly by tubular creatinine secretion. In this study, we monitored creatinine clearance (Ccr), GFR on the basis of polyfructosan renal clearance (Cpf) and parameters characterizing tubular creatinine secretion (Ccr/CpF, Ccr - Cpf, Tcr/CpF x 100) in 12 individuals with renal grafts (Group A), 12 kidney graft donors for related transplantation (Group B), and in 27 individuals undergoing nephrectomy for a pathological process in one kidney (Group C). In the monitored groups, Cpf and Ccr values were within the limits consistent with the normal function of a single kidney in a healthy individual. The values characterizing tubular creatinine secretion in Group A did not differ significantly from those obtained in Groups B and C. However, the parameters showed a wide range in all groups. In seven individuals with a renal graft, all the above functional parameters were monitored at three-month intervals for a period of 24 months. Significant differences in the time courses of Cer and Cpf due to marked intra-individual fluctuations were found in tubular creatinine secretion. The findings suggest that the rate of tubular creatinine secretion in the renal graft does not differ significantly from that in individuals with a single native (normally functioning) kidney. However, there are large inter-individual differences. The large intra-individual fluctuations in tubular creatinine secretion in the kidney graft result in significant differences in the time courses of Cer and Cpf and a possibility of erroneous evaluation of graft function if based exclusively on Cer.